Rocker arm

ABSTRACT

A rocker arm for a type III valve train assembly for an internal combustion engine includes: a roller follower for following a cam in use; a roller axle about which the roller follower rotates in use; a biasing means holder, the biasing means holder being connected to the roller axle for sliding movement relative to the roller axle over a fixed distance, the biasing means holder contacting a reaction component in use; and a biasing means arranged to bias the biasing means holder away from the roller axle. The rocker arm is arranged such that, in use, sliding movement of the biasing means holder relative to the roller axle when the biasing means holder contacts the reaction component when a lift profile of the cam engages the roller follower causes the biasing means to compress and thereby to urge the roller follower into contact with the cam.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2018/086434, filed on Dec. 20, 2018, and claims benefit to British Patent Application No. GB 1721554.2, filed on Dec. 21, 2017. The International Application was published in English on Jun. 27, 2019 as WO 2019/122263 under PCT Article 21(2).

FIELD

The present invention relates to a rocker arm, and more specifically to a rocker arm for a type III valve train assembly for an internal combustion engine.

BACKGROUND

Internal combustion engines comprise valve train assemblies. Valve train assemblies may comprise rocker arms for controlling opening and closing of valves the engine, i.e. intake or exhaust valves of a cylinder of an internal combustion engine. One type of valve train is a so-called type III valve train. A type III valvetrain comprises a single overhead cam (SOHC) arrangement. In a known type III valvetrain, a rocker arm is mounted on a rocker shaft, and a cam shaft comprises a cam arranged to engage with a first end of a rocker arm to cause the rocker arm to pivot about the rocker shaft, thereby to cause a second end of the rocker arm to push against a valve stem of a valve, thereby to cause a valve opening event.

It may be desirable to control or maintain a constant lash (i.e. clearance or total clearance between components of the valve train assembly) in type III valve train assemblies. A rocker arm with an adjustable system allows for adjustment of the lash, for example to absorb the stack up of dimensional tolerances in the valve train resulting from components thereof. However, such adjustment can lead to an increased engine assembly time. In addition, the adjustment system is susceptible to wear and may have to be re-adjusted during standard services.

SUMMARY

In an embodiment, the present invention provides a rocker arm for a type III valve train assembly for an internal combustion engine, the rocker arm comprising: a roller follower configured to follow a cam in use; a roller axle about which the roller follower is configured to rotate in use; a biasing means holder, the biasing means holder being connected to the roller axle for sliding movement relative to the roller axle over a fixed distance, the biasing means holder being configured to contact a reaction component in use; and a biasing means arranged to bias the biasing means holder away from the roller axle, wherein the rocker arm is configured such that, in use, sliding movement of the biasing means holder relative to the roller axle when the biasing means holder contacts the reaction component when a lift profile of the cam engages the roller follower causes the biasing means to compress and thereby to urge the roller follower into contact with the cam.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. Other features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following:

FIG. 1 illustrates schematically a side view of a portion of a valve train assembly according to an example.

DETAILED DESCRIPTION

In an embodiment, the present invention mitigates at least some of the deficiencies of the prior art.

Referring to FIG. 1, there is illustrated a valve train assembly 10 comprising a rocker arm 5 according to an example. The valve train assembly 10 is a type III valve train assembly, in a single overhead cam (SOHC) arrangement (the cam is not shown in FIG. 1). The rocker arm may be referred to as a type III rocker arm. The valve train assembly 10 comprises a camshaft comprising a cam, comprising a lift profile and a base circle.

The rocker arm 5 comprises, at a first end 26 of the rocker arm 5, a roller follower 24 for following the cam in use. The rocker arm 5 comprises a roller axle 28 on which the roller follower 24 is mounted, and about which the roller follower 24 is arranged to rotate in use. The axis of rotation of the roller follower 24 is the roller axis 6. The rocker arm 5 is itself mounted on a rocker shaft, and is arranged to pivot about the rocker shaft, about a rocker shaft axis 4. A second end of the rocker arm 5, opposite to the first end 26 of the rocker arm 5, is for contacting a valve (an exhaust or intake valve) of the overall internal combustion engine. The rocker arm 5 may comprise at the second end for example a component for compression engine braking, and hence the rocker arm 5 may be, for example, configured for compression engine braking, or for example, part of a compression engine braking system, for example.

In general overview, when the roller follower 24 engages the lift profile of the cam, the cam causes the rocker arm 5 to pivot about the rocker shaft axis 4 (clockwise in the sense of FIG. 1), which in tum may cause the second end of the rocker arm 5 to push down on a valve stem of a valve of a cylinder of the internal combustion engine thereby for example to cause a valve opening event.

The rocker arm 5 comprises a biasing means 3 and a biasing means holder 7. In this example, the biasing means 3 is a bias spring 3, and the biasing means holder 7 will be referred to as a bias spring holder 3 accordingly.

The bias spring holder 7 is connected, at a first 7 a end, to the roller axle 28 for sliding movement relative to the roller axle 28 over a fixed distance. Specifically, the bias spring holder defines at least one elongate slot 32 in which the roller axle 28 is slidably disposed. The slot 32 comprises closed ends 32 a and 32 b. The roller axle 28 may travel in the slot 32 between the closed ends 32 a, 32 b.

The bias spring holder 7 comprises at a second end 7 b, opposite to the first end 7 a, a holding portion 36 for supporting a first end 3 a of the bias spring 3. The second end 7 b of the bias spring holder 7 is also arranged for contacting a reaction component 2 of the valve train assembly in use. The reaction component 2 may be, for example a bar 2 or the like and may be fixed relative to, for example fixed to, the engine cylinder head.

A second end of the bias spring 3 is engaged with the roller axle 28. The bias spring 3 is arranged to bias the bias spring holder 7 away from the roller axle 28. The extent to which the bias spring holder 7 is biased away from the roller axis 28 is limited by the roller axle 28 engaging with the first closed end 32 a of the slot 32 of the bias spring holder 7.

When the roller follower 24 is engaged with the base circle of the cam, there is a bias spring lash or gap 1 between the reaction component 2 and the second end 7 b of the bias spring holder 7. This is the situation illustrated in FIG. 1. In other words, when the roller follower 24 is engaged with the base circle of the cam, the bias spring holder 7 is preloaded against the roller axle 28 by the bias spring 3, and the first closed end 32 a of the slot 32 of the bias spring holder 7 contacts the roller axis 28 to act as a hard stop, hence defining the maximum distance of the second end 7 b of the bias spring holder 7 from the roller axle 28. This maximum distance sets the lash or gap 1 between the reaction component 2 and the second end 7 b of the bias spring holder 7 when the roller follower 24 is engaged with the base circle of the cam. The bias spring lash 1 between the reaction component 2 and the bias spring holder 7 may therefore be precisely defined thereby, and hence may not need adjustment, hence saving installation time and reducing costs.

When the lift profile of the cam engages the roller follower 24, the bias spring holder 7 contacts the reaction component 2, and the bias spring holder 7 is thereby moved relative to the roller axle 28 to compress the bias spring 3, and as a result, the roller follower 24 is urged into contact with the cam. In other words, sliding movement of the bias spring holder 7 relative to the roller axle 28 when the bias spring holder 7 contacts the reaction component 2 when the lift profile of the cam engages the roller follower 24 causes the bias spring 3 to compress and thereby to urge the roller follower 24 into contact with the cam. More specifically, during the opening ramp of cam lift events (i.e. when the initial ramp of the lift profile of the cam engages the roller follower 24, the rocker arm 5 rotates about the rocker shaft axis 4 (clockwise in the sense of FIG. 1) and the bias spring holder 7 makes contact with the reaction component 2. As a result, the first closed end 32 a of the slot 32 of the bias spring holder 7 bias spring holder loses contact with the roller axle 28 as the roller axle 28 moves up the slot 32 (for example up the slot 32 until the second closed end 32 b), and the bias spring 23 is compressed between the roller axle 28 and the holding portion 36 or the bias springholder 7. As a result, a load is asserted to the cam/roller interface ensuring contact between the two. That is, the bias spring when compressed urges the rotation of the rocker arm 5 anticlockwise in the sense of FIG. 1, against the cam, to urge the roller follower 24 into contact with the cam.

The urging of the roller follower 24 into contact with the cam during portions of the engine cycle when the lift profile of the cam is engaging the roller follower 24 may help ensure proper positioning of the rocker arm 2, and hence may help prevent or mitigate faults.

When the roller follower 24 again engages with the base circle of the cam, that is, when the roller follower 24 returns to the cam base circle on the closing ramp of the lift profile, the bias spring 3 extends, the first closed end 32 a of the slot 32 of the bias spring holder 7 bias spring holder 7 makes contact with the roller axle 28 again, and the bias spring lash 1 is again re-established. The bias spring holder 7 therefore may have only intermittent contact with the reaction component 2.

The bias spring holder 7 being anchored to the roller axle 28 allows that the maximum height of the bias spring holder relative to the roller follower 24, and to the base circle of the cam, may be precise enough to remove any need for need for adjustment of the lash 1. The rocker arm 5 may therefore be installed into the cylinder head assembly and on doing so may immediately have a bias spring lash 1 within a tolerable range, and hence may remove the need to adjust the bias spring holder 7 or rocker arm 22 to provide a bias spring lash 1 in a tolerable range, as with an existing system. The need for readjustment during engine service may also be eliminated. Assembly and service time may both therefore be reduced and hence cost may be reduced.

As described above, the type III valvetrain bias spring holder 7 has a fixed maximum length (i.e. a fixed maximum displacement relative to the roller axis 6 of the rocker arm 22). This may be as compared for example to adjustable systems that are adjustable to set the bias spring lash within a specified range. The adjustment is to absorb the stack up of dimensional tolerances that results from attachment of a bias spring holder to features unrelated to the rocker shaft axis. The adjustment can increase engine assembly time, and the adjustment system is susceptible to wear and may have to be re-adjusted during standard services. In examples of the present invention however, the bias spring holder 7 has a precise, fixed maximum length due to its direct relation to the roller axis 6 and so does not need adjustment during assembly, thus saving assembly time. The bias spring holder maintains a constant lash or gap 1 between the bias spring holder 7 and the neighbouring reaction component or components 2 in the cylinder head whilst on the cam base circle, and the bias spring holder 7 makes contact with the reaction component 2 during cam lift (i.e. whilst on the lift profile of the cam), compressing the bias spring (3) and ensuring cam-to-roller contact.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments.

The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C. 

1. A rocker arm for a type III valve train assembly for an internal combustion engine, the rocker arm comprising: a roller follower configured to follow a cam in use; a roller axle about which the roller follower is configured to rotate in use; a biasing means holder, the biasing means holder being connected to the roller axle for sliding movement relative to the roller axle over a fixed distance, the biasing means holder being configured to contact a reaction component in use; and a biasing means arranged to bias the biasing means holder away from the roller axle, wherein the rocker arm is configured such that, in use, sliding movement of the biasing means holder relative to the roller axle when the biasing means holder contacts the reaction component when a lift profile of the cam engages the roller follower causes the biasing means to compress and thereby to urge the roller follower into contact with the cam.
 2. The rocker arm according to claim 1, wherein the biasing means holder defines at least one slot in which the roller axle is slidably disposed.
 3. A valve train assembly of an internal combustion engine, the valve train assembly comprising: the rocker arm according to claim 1; the reaction component; and the cam, wherein the valve train assembly is configured such that, in use, when the roller follower engages a base circle of the cam, there is a lash between the reaction component and the biasing means holder, and when a lift profile of the cam engages the roller follower, the biasing means holder contacts the reaction component to move the biasing means holder relative to the roller axle to compress the biasing means thereby to urge the roller follower into contact with the cam. 